The present invention relates to a scanning exposure method, a scanning exposure apparatus and making method thereof, and a device and a device manufacturing method. More particularly, the present invention relates to a scanning exposure method to be employed in a lithographic process for manufacturing a semiconductor device, a liquid crystal display device and so forth; a scanning exposure apparatus on which the scanning exposure method is applied and a making method thereof; as well as a device which is manufactured by using the scanning exposure apparatus and a manufacturing method thereof.
Conventionally, in a lithographic process for manufacturing a semiconductor device, liquid crystal display device and so forth, an exposure apparatus has been used. In such an exposure apparatus, patterns formed on a mask or reticle (to be genetically referred to as a xe2x80x9creticlexe2x80x9d hereinafter) are transferred through a projection optical system onto a substrate such as a wafer or glass plate (to be referred to as a xe2x80x9csubstrate or waferxe2x80x9d herein after, as needed) coated with a resist or the like. In general, a projection optical system with a large numerical aperture (to be referred to as xe2x80x9cN.A.xe2x80x9d, hereinafter) and a shallow focal depth is used in the projection exposure apparatus. The mechanism to bring the substrate surface to a proximate level of an imaging plane in the projection optical system is necessary for the projection exposure apparatus for transferring fine circuit patterns onto a substrate with high resolution. Therefore, the exposure apparatus has a focusing system for brining the substrate surface to the range of the focal depth of the projection optical system. The system is composed of the focus/leveling detecting mechanism and the adjusting mechanism, and the system is referred to as the xe2x80x9cZ-leveling stagexe2x80x9d herein after. The focus/leveling detecting mechanism detects the position and tilt of the substrate surface in optical axis direction of the projection optical system (that is, Z-direction), and the adjusting mechanism adjusts the position and the posture of the substrate surface by using the detected position and the tilt of the surface in Z-direction.
On the contrary, semiconductor chip devices recently tend to be large-sized, and there is needs to transfer larger patterns onto the substrate by the projection exposure. For satisfying such needs, so-called step and scan type scanning exposure apparatus is practically used. In the apparatus, a reticle and the substrate are synchronously scanned against the projection optical system, shot areas are exposed over the effective illumination area of the projection optical system. In the scanning type exposure apparatus, in order to expose a shot area on the substrate surface, the shot area, i.e. substrate, and the reticle must be moved synchronously with the fixed velocity commensurate to the predetermined exposure dose amount, while the substrate and the reticle are positioning. Therefore, the following procedures are included: the stage on which the substrate is loaded (XY stage) is allowed to run when the shot area is far from exposure area on the substrate surface, on which exposure light is illuminated when the light is passed through the projection optical system; the stage loading the substrate and the stage loading the reticle are synchronized; and then, the exposure is begun at the time that the shot area on the substrate is reached the exposure area.
As a part of the procedure, the positional information in Z-direction and the tilt information in the synchronized moving direction and the unsynchronized moving direction (i.e., perpendicular to the synchronized direction) are detected for the substrate surface area in the exposure area. By using this detection result, the focusing operation is performed for the substrate surface area in the exposure area. In the focusing operation, the focusing operation for focusing in the optical axis direction of the projection optical system (Z-direction) and the leveling operation for focusing in tilt direction around X-axis and Y-axis are simultaneously performed. Thereby, the difference between the expose plane on the substrate and the image plane of the projection optical system becomes minimal. When the synchronous moving direction is Y-direction, the tilt for the synchronous moving direction is represented as the rotational amount around X-axis, and that in the asynchronous moving direction is represented as the rotational amount around Y-axis.
In the step and scan type scanning exposure apparatus, since the substrate to be exposed is moved during the exposure, the control is repeated successively so that the image plane of the projection optical system closes to the exposure plane on the surface of the photosensitive substrate. Accordingly, in the typical structure of the Z-leveling stage in which the driving mechanism is arranged periphery of the substrate, most of the driving load in the leveling stage is caused by the leveling operation.
In such scanning exposure apparatuses, the slit shape of the exposure area on which the exposure light passed through the projection optical system is generally In the shape of the exposure area, the length in the synchronous moving direction (for example, Y-direction) is shorter than that in the asynchronous moving direction (for example, X-direction). Based on the shape of the exposure area, focus detection points are arranged inside of the exposure area (and outside of it, if necessary). At that time, the length that is used as the base line for calculating the tilt components in the synchronous moving direction is shorter than that in asynchronous direction. Therefore, the leveling action for the asynchronous direction greatly contributes to the driving load on the Z-leveling stage.
That is, in the step and scan type scanning apparatus, most of the driving practicability of the Z-leveling stage is spent to the leveling action in the scanning direction.
Integrated circuit patterns formed on the substrate often have different number of starts, and it causes the increase of driving load for the Z-leveling stage in the leveling action for the synchronous moving direction. In the substrate having such different number of stairs, the stair pattern formed by the different number of stairs sometimes has the periodical repeating components. Furthermore, the distribution state of the period varies depending on, for example, the application or characteristics of the integrated circuit pattern. When the ratio of the short periodical components is high, the driving load for the leveling action in the synchronous moving direction. Therefore, the driving practicability of Z-leveling stage should be high must, and it causes the structure of Z-leveling stage to be complicate and large scaled.
When the performance of z-leveling stage does not fulfill the required performance for following-up the leveling in the synchronous direction, the adjustment of the leveling is insufficient. Furthermore, when 100% of the performance of Z-leveling stage is applied for following-up the leveling caused by the difference number of the stairs in the synchronous moving direction, it is impossible to correct the figure of the substrate except the difference (for example, warpage or swell in the raw substrate). Thereby nonlinear area is generated which causes to loose control, and the transfer of the pattern can be affected by more serious effect such as awful deterioration for imaging and so forth.
The present invention has been made in consideration of the above-mentioned situation. The first object of the present is to provide the exposure method for transferring a pattern without extreme deterioration of the imaging performance.
The second object of the present invention is to provide the exposure apparatus for transferring a pattern without extreme deterioration of the imaging performance.
The third object of the present invention is to provide the device on which fine patterns are precisely formed.
As mentioned above, in the scanning exposure by the so-called step and scan member, high focusing driving power is necessary as the premise for accurate focusing control at respective time point during exposure by followed-up the synchronous moving. According to the knowledge from the study conducted by the present inventors, the exposure area to be illuminated by the exponent light generally has a certain slit with in the synchronous moving direction. Therefore, when the period of the convex and concave in the divided area on the substrate surface having the difference of a stair is shorter than the slit width, the imaging performance is not improved by amending the leveling in the synchronous moving direction to follow-up the difference of the stair.
That is, when the repeating period of the difference on the substrate is shorter than the slit width, the defocus amount in the part around the center is run into almost 0 by the follow-up of the leveling in the synchronous moving direction. However, around of the edge of the exposure area is exposed under the condition that rather large defocus amount resides (see FIG. 9A). In this case, as shown in Japan laid-open No. S63-64037 and its corresponding U.S. Pat. No. 4,869,999, the superimposed focal exposure, in which the decline of the focal depth is amended by the superimposing projected images at different focus positions, is performed. In the superimposed focal exposure, the exposure is performed with three conditions of the positive defocus amount/no defocus amount/negative defocus amount. On the contrary, when the follow-up of the leveling in the synchronous moving direction is not used, the defocus amount in the part around the center of the exposure area is almost 0. Except the part around the center of the exposure area is exposed under the condition in which the defocus amount in proportion to the distance from the center remains (see, FIG. 9B). In this case, as shown in Japan laid-open No. H5-13305 and its corresponding U.S. Pat. No. 5,343,270, the continuous superimposed exposure from the positive defocus amount to the negative one is performed.
Since various parameters such as the photoresist agents and so forth are related, it is case by case that either one give results that are most desirable in brief. However, when the leveling is followed-up, Z-leveling stage is applied more load. Therefore, on the design of the apparatus, Z-leveling stage must be designed to have larger margin in its performance. Being estimated shorter the period of the difference of the stair in the substrate, being clearer the tendency.
The present invention is completed based on the above description. In the first aspect of the present invention, the present invention is the scanning exposure method for transferring a pattern formed on a mask to a divided area on a substrate through a projection optical system, while said mask and said substrate are synchronously moved, comprising the steps of: deciding a focusing control mode to be used when said pattern is transferred onto the divided area in a plurality of focusing control modes, depending on a surface condition of the divided area; transferring the pattern formed on the mask onto the divided area and performing said focusing control in the decided mode.
With this, the mode of the focusing control is decided, depending on the surface condition of the divided area. Then, the pattern formed on the mask is transferred onto the divided area, performing the focusing control with the properly adjusted mode Accordingly, the properly adjusted focusing control action might be performed, depending on the surface condition of the divided area in which the warpage or swell of the raw substrate is reflected. Therefore, the pattern formed on the mask is transferred onto the substrate with no serious deterioration of the imaging performance or no premise for the high driving practicability for the focusing control (to be referred to as the xe2x80x9cfocusing control driving powerxe2x80x9d).
The focusing control might include the focus position control that controls the position of the substrate in the optical axis direction of the projection optical system. In addition, it might include the leveling control that controls the tilt of the substrate to the plane perpendicular to the optical axis direction of the projection optical system. The leveling control might include the tilt control of the substrate in the synchronous moving direction and the tilt control of the substrate in the direction perpendicular to the synchronous moving direction in the plane perpendicular to the optical axis direction of the projection optical system.
In the first scanning exposure direction, the focusing control mode to be used when said pattern is transferred might be decided, further considering a shape of an illumination area on said substrate. Alternatively, the focusing control mode can be decided, prior to the transfer operation for the divided area. In this case, the focusing control mode for the substrate is decided depending on the relation between the surface condition of the divided area and the shape of the illumination area (the exposure area). Then, the pattern formed on the mask can be transferred onto the divided area, performing the focusing control in the properly adjusted mode.
The leveling control can be done or not done by taking notice of that in the synchronous moving direction, in which it is predicted that the driving load becomes the highest when the focusing control is performed. That is, the plurality of focusing control mode include: the first mode in which the tilt control of the substrate is performed in the synchronous moving direction by following-up the synchronous moving; and a second mode in which tilt control of the substrate is not performed in the synchronous moving direction by following-up the synchronous moving.
Furthermore, the surface condition of the divided area can be represented as a spatial frequency distribution along the synchronous moving direction of the substrate, on which a repeating unit area of the pattern to be transferred having convex and concave along the optical axis direction of the projection optical system, wherein the repeating unit area is placed in said divided area; and the shape of the illumination area is represented as a slit width of the illumination area in the synchronous moving direction of the substrate. Then, the substrate can be controlled by the focusing control in the first mode or the second mode. The first mode is used, when a predominant wavelength is equal to or longer than the length depending on the slit width, wherein the predominant wavelength is corresponding to a predominant frequency, which has maximum amplitude in said spatial frequency distribution. The second mode is used, when a predominant wavelength is shorter than the length depending on the slit width. In this case, the leveling control in the synchronous direction can be the suitable control that neither has serious deterioration of the imaging performance nor requires high focusing control power, when the high driving load is supposed to be necessary for the focusing control.
The length depending on the slit width can be the slit width.
In the first scanning exposure method, for example, the surface condition of the divided area can be obtained by calculating based on the lithography process for the substrate, or can be measured prior to the transfer of the pattern formed on the mask onto the divided area.
Such a prior measurement can be conducted in every lot of the substrate, prior to the transfer of the pattern. Alternatively, it can be done in every exposure process, prior to the transfer of the pattern. Furthermore, when a plurality of the divided areas are arranged on the substrate, the prior measurement for the surface condition of the substrate can be representatively conducted for one of the divided areas. In the above-mentioned cases, the time to be spent the prior measurement can be shorten without the large transfer error of the pattern, compared to perform the prior measurement for the surface condition of every divided area.
In the first scanning exposure method, the focusing control might include a focus position control that controls a position of said substrate in an optical axis direction of said projection optical system; on a decision that said focus position control can not follow-up said synchronous moving, a control, wherein a position of the substrate in an optical axis direction of said projection optical system just prior to the decision is maintained, is performed. In this case, the pattern formed on the mask is transferred onto the substrate with no serious deterioration of the imaging performance or no premise for the high driving power for the focusing control.
In the first scanning exposure method, the focusing control can include a tilt control of the substrate in the synchronous moving direction; on a decision that the tilt control can not follow-up said synchronous moving, a control, wherein a position of the substrate in an optical axis direction of said projection optical system just prior to the decision is maintained, is performed. When it is decided that the synchronous moving can be followed-up the tilt control, the tilt control is performed by following the synchronous moving. In this case, the leveling control in the synchronous direction can be the suitable control that neither has serious deterioration of the imaging performance nor requires high focusing control power, when the high driving load is supposed to be necessary for focusing control.
Alternatively, in the first scanning exposure method, the said focusing control includes a tilt control that controls the tilt of the substrate, wherein the substrate is moved in a plane perpendicular to the optical axis direction of the projection optical system and the tilt of the substrate in a direction perpendicular to the synchronous moving direction is controlled; on a decision that the tilt control can not follow-up said synchronous moving, a control, wherein a position of the substrate in an optical axis direction of said projection optical system just prior to the decision is maintained, is performed. When it is decided that the synchronous moving can be followed-up the tilt control, the tilt control is performed by following the synchronous moving. In this case, the leveling control in the synchronous direction can be the suitable control that neither has serious deterioration of the imaging performance nor requires high focusing control power, when the high driving load is supposed to be necessary for the focusing control.
In the second aspect of the present invention, the present invention is the second scanning exposure method for exposing the substrate, while moving the substrate in a predetermined direction to an exposure beam which passes through the projection optical system, and detecting a position information of the substrate surface in the optical axis direction of the projection optical system comprising the steps of: measuring convex and concave information on the substrate surface, while moving the substrate in the predetermined direction in a condition that the substrate is not exposed; and deciding whether a tilt of the substrate in the predetermined direction is adjusted or not, during an exposure of the substrate, by using said a convex and concave information measured, wherein based on said position information detected.
With this, while the substrate is moved into the predetermined direction with no exposure, the information of the concave and convex on the substrate surface is measured. Based on the detection result of the concave and convex, it is decided whether a tilt of the substrate in the predetermined direction, which is obtained from the position information of the substrate surface in the optical axis direction of the projection optical system, is adjusted or not. Accordingly, the pattern formed on the mask might be transferred onto the substrate, performing the suitable focusing control depending on the surface condition of the divided area.
In the second scanning exposure method of the present invention, it can be decided whether a tilt of the substrate in the predetermined direction is adjusted or not during an exposure of the substrate so that a deterioration of positioning accuracy of the image plane of said projection system and the substrate surface is prevented. In this case, the properly adjusted focusing control action might be performed, depending on the surface condition of the divided area in which the warpage or swell of the raw substrate is reflected. Therefore, the pattern formed on the mask is transferred onto the substrate with no serious deterioration of the imaging performance or no premise for the high driving power for the focusing control.
In the third aspect of the present invention, the present invention is the scanning exposure apparatus which is used to transfer the pattern formed on the mask onto the divided area on the substrate, through a projection optical system, moving the mask and the substrate, comprising: a mask stage for holding the mask; a substrate stage for holding the substrate; the first detecting system for detecting a position for at least one of detection point in an optical axis direction of the projection optical system, in a illumination area on said substrate surface; the first driving system for driving the mask stage and the substrate stage in plane perpendicular to the optical axis direction of the projection optical system; the second driving system for driving the substrate stage to at least one of the optical axis direction of the projection detecting system and the tilt direction; a memory unit for storing a data representing the substrate condition of the divided area; and a control system for synchronously moving the mask stage and the substrate stage by controlling the first driving system, while performing said focusing control by controlling the second driving system based on a result from the first detecting system, wherein a focusing control mode to be used in the transfer a pattern onto said divided area is decided from a plurality of focusing control modes based on the data representing the substrate surface of the divided area.
According to this, the control system decides a focusing control mode based on a relation between a data representing the substrate surface of the divided area and a data for the shape of the illumination area. Then, the control system controls the second driving system in the decided focusing control mode, based on the detection result from the first detecting system to drive the substrate stage for holding the substrate into the optical axis direction of the projection optical system, to performs the focusing control. In company with the focusing control, the control system controls the first driving system to perform synchronous moving control of the mask stage and the substrate stage; thereby the pattern formed on the mask is transferred onto the divided area on the substrate through the projection optical system. Accordingly, the pattern is transferred by using the present exposure method, it can be transferred without serious deterioration of the imaging performance, while the focus control is performed by using the simple structure which does not promise the high focusing driving practicability. Alternatively, the control system can be structured so that the focusing control mode is decided, prior to the transfer operation for the divided area.
In the focusing control, the structure might be used; wherein the control system performs the focus position control, which control is the second driving system by using the detection result from the first detecting system according to the decided focusing control mode, and it includes the focusing control for controlling the substrate position in the optical axis direction of the projection optical system. The other structure might be used; wherein the first detecting system for detecting the position of the multiple detection points, and the control system for performing the focusing control including the leveling control. In the first detecting system, the multiple detection points include at least two detection points in the illumination area on the substrate, and the positions of them in the optical axis direction of the projection optical system are detected. The leveling control controls the second driving system by using the detection result from the first detecting system according to the decided focusing control mode, and it controls the tilt of the substrate to the plane perpendicular to the optical axis direction of the optical projection system.
In the leveling control, the structure might be used: wherein the first detecting system detects the positions of the multiple detection points in the illumination area on the substrate surface in the optical axis direction of the projection optical system; and the multiple detection points include at least two points, of which positions in the synchronous moving direction are different. The control system controls the second driving system by using the detection result from the first detecting system according to the decided focusing control mode to perform leveling control including the tilt control of the substrate in the synchronous moving direction. Furthermore, another structure might be used; wherein the first detecting system detects the positions of the multiple detection points in the illumination area on the substrate surface in the optical axis direction of the projection optical system; and the multiple detection points include at least two points, of which positions in the direction perpendicular to the synchronous moving direction are different. The control system controls the second driving system by using the detection result from the first detecting system according to the decided focusing control mode to perform the leveling control including the tilt control of the substrate in the plane perpendicular to the synchronous moving direction.
In the scanning exposure apparatus of the present invention, the above-mentioned control system might be the structure for deciding the focusing control mode based on the relation between the data representing the surface condition of the divided area and that for the shape of the illumination area. In this case, since the focusing control mode is decided, further considering the shape of the illumination area on the substrate surface, the suitable focusing mode is precisely decided.
The plurality of focusing control modes can be include: the first mode for controlling a tilt of the substrate in the synchronous moving direction by following-up the synchronous moving of the substrate; and the second mode for not controlling the tilt of the substrate in the synchronous moving direction by following-up the synchronous moving of said substrate. Furthermore, the following structure can be used: wherein, the data representing the substrate surface on the divided area is a predominant wavelength corresponding to a predominant frequency, of which amplitude is maximal in a spatial frequency distribution. The distribution shows a repeating unit area for the pattern to be transferred in the divided area having a convex and concave on the substrate. Wherein, the convex and concave are in the synchronous direction. The data for the shape of the illumination area is a slit width in the synchronous moving direction of the illumination area; and the control system performs the focusing control of the substrate in the first mode when the predominant wavelength is not shorter than the slit width, and it performs the focusing control of the substrate in the second mode when the predominant wavelength is shorter than the slit width.
The scanning exposure apparatus can be further comprise the second detecting system which detects a tilt of the substrate stage in the synchronous moving direction to a virtual plane perpendicular to the optical axis direction of the projection optical system and in a direction perpendicular to the said synchronous moving direction; and the main control system can perform the focusing control based on detection results from the first and second detecting systems. With this, when the suitable focusing control can be performed by using the detection result from the first detecting system, the suitable focusing control can be performed by further considering the detection result from the second detecting system.
The following structure can be used: when a plurality of focusing control modes further includes a third mode, which maintains the surface of the substrate shape in parallel with the virtual plane based on the detection result from the second detecting system. The exposure apparatus further comprises the calculating operation unit, which acquires the detection result data from the first detecting system during the synchronous moving under the focusing control in the third mode and then obtain the surface condition of the divided area, based on the detection result data. In this case, adding to the general exposure processing, the measurement processing for the surface condition of the divided area prior to the scanning exposure by itself. Alternatively, the calculating operation unit employs the structure; wherein the calculating operation unit calculates the spatial frequency distribution formed by the concave and convex along the synchronous moving direction of the substrate, and the calculating operation units obtains a predominant wavelength corresponding to a predominant frequency which becomes maximum in the spatial frequency distribution to store in the memory unit, and then an calculating operation system for acquiring a detection result data by using the first detecting system during said synchronous moving under the focusing control in the third mode, and it obtains the surface condition of the divided area based on the detection result data. Wherein, the concave and convex in the optical axis direction of the projection optical system are formed in the area for repeating unit of a pattern to be transferred in the divided area.
In the fourth aspect of the present invention, the present invention is a making method of a scanning exposure apparatus for transferring the pattern formed on the mask through a projection optical system, while a mask and a substrate move synchronously, comprising the steps of: providing a mask stage for holding the mask; providing a substrate stage for holding the substrate; providing a first detecting system for detecting a position of the projection optical system in an optical axis direction in at least one detection point in said illumination area on the substrate surface; providing a first driving system for driving the mask stage and the substrate stage in a plane which is perpendicular to the optical axis direction of the projection optical system; providing a second driving system for driving the substrate stage in at least one direction of the optical axis direction of the projection optical system or a tilt direction; providing a memory unit for memorizing a data representing a surface condition of the divided area; and providing a control system for moving the mask stage and the substrate stage synchronously by controlling the first driving system, performing the focusing control by controlling the second driving system based on a result from the first detecting system. Alternatively, the control system can use the structure in which the focusing control mode is decided, prior to the transfer operation for the divided area.
With this, the exposure apparatus of the present embodiment might be produced; wherein, the above-mentioned mask stage, the substrate stage, the first detecting system, the first driving system, the second driving system, the memory unit, control system, and other blocks and units, and are connected electrically, mechanically and optically to assemble the apparatus. After that, the apparatus is totally adjusted (electrical adjustment or inspection of the operation).
The making method of the scanning type exposure apparatus of the present invention can further comprise the step of providing the second detecting system for detecting a tilt of the substrate stage in the synchronous moving direction to a virtual plane perpendicular to the optical axis direction of the projection optical system and in a direction perpendicular to the synchronous moving direction. In this case, the apparatus for performing the suitable focusing control can be made, which performs the suitable focusing control by considering the detection result from the second detecting system, even when the suitable focusing control can not be performed based on the sole detection result from the first detection system.
The making method of the scanning type exposure apparatus of the present invention for providing the second detecting system might further comprise the step of providing a calculating operation system for acquiring a detection result data from the first detecting system during the synchronous moving under the focusing control, which maintains the substrate stage surface to be substantially parallel to the virtual plane, based on the detection result from the second detecting system to obtain the surface condition of the divided area.
Furthermore, in the lithography step, the device comprising fine patterns may be manufactured by transferring a predetermined pattern to the divided area formed on the substrate by using the apparatus of the present invention. At that time, the exposure method in which the first or the second position detection method described above is used. Accordingly, the present invention is the device manufactured by using the exposure apparatus of the present invention in another viewpoint, and also it is the manufacturing method of device by using the exposure method of the present invention to transfer the predetermined pattern onto the substrate.